This invention relates to microelectronic devices, and, more particularly, to such a device moved from one substrate to another during fabrication.
Thin-film microelectronic devices are fabricated on a substrate, typically a thin piece of a single-crystal material such as silicon. The microelectronic circuitry is formed in the substrate by a combination of steps such as deposition, implantation, film growth, etching, and patterning. In these steps, patterned layers of metals, semiconductors, and insulators are created on or near the surface of the substrate with the physical arrangements, interfaces, and structures required for individual circuit components and the electrical leads that extend between them.
The substrate performs important roles in the fabrication and use of the microelectronic device. The lattice matching between the substrate and the layer deposited upon the substrate strongly influences the structure, orientation, and operability of that layer in the device. The chemical composition (i.e., doping) of the substrate can also play a major role in the operability of the device.
Microelectronic devices are normally assembled together with other components into higher-level structures and packages. The substrate used for the microelectronic device also plays an important role in product performance after the subsequent assembly of the device into such higher-level products. These complex electronic structures are often heated and cooled during storage and service. For example, sensors often must be operated at cryogenic temperatures, necessitating the cooling of the final assembled structure of sensor element and electronic device to such low temperatures. If the substrate of a particular microelectronic device has a substantially different coefficient of thermal expansion than other structure s with which it is assembled to make the final product, thermal expansion stresses and strains are created. If the thermal expansion mismatch is too large, the thermal stresses and strains may adversely affect the operation of the microelectronic device, and, in the extreme case, cause a mechanical failure of the structure.
A great deal of effort has been devoted to selecting combinations of materials and structures that permit fabrication of microelectronic circuitry having the required structure and electronic performance In the fabricated microelectronic device, and at the same time minimize adverse effects of thermal expansion mismatch in the final structure. This search for operable combinations is limited by the available materials provided by nature. In some instances suitable combinations simply have not been found, or the best available combinations are only marginally acceptable.
There remains a need for further improvements in the fabrication of microelectronic devices, with specific reference to these problems of fabricability and subsequent performance of the devices. The present invention fulfills this need, and further provides related advantages.